This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 101 07 558, filed on Feb. 17, 2001, the entire disclosure of which is incorporated herein by reference.
The invention relates to an apparatus for dosing a lubricant such as oil, grease or the like into a compressed air line, whereby the apparatus includes a lubricant container, a lubricant pump, and at least one valve.
A great variety of different dosing devices are known in the prior art, for dosing or dispensing small controlled quantities of lubricant into a compressed air line, for example. Such dosing devices are also known as injection oilers or minimum quantity dosing systems. The general technology of these systems is based on an air injection and spraying system, wherein a predetermined quantity of a lubricant is injected into a compressed air flow, by which the lubricant is then sprayed or blown with a suitable pressure onto the machine part or other component that is to be lubricated. Such lubricant dosing devices are used for a variety of different applications in a variety of different fields. Examples of dosing devices of this kind are sold commercially in ordinary trade by the company Willy Vogel AG, Berlin, Germany.
All conventionally available dosing systems of the above described general type usually have many features and parameters that can be adjusted by the user or operating personnel, for example offering the possibility of adjusting the quantity of lubricant to be injected during each dosing cycle. In view of this broad adjustability, it is possible to make faulty or improper adjustments, and to mechanically tamper with the device. That very easily leads to operating errors, so that a reliable and proper lubricating operation cannot be ensured. Moreover, monitoring and controlling the proper functionality, and recognizing any arising errors or faults during the lubricating process is not possible, or is only possible with considerable technical efforts.
Overall, the handling, error monitoring, identification and correction, the great number of individual parts, and the complicated arrangement and connection of the various lines or conduits of such conventionally available systems are not suitable for reliably achieving a minimum error rate. Depending on the particular application, a defect of the dosing system which causes an improper or inadequate lubrication can lead to faulty operation or even a total failure and breakdown of the apparatus or machine that is to be lubricated by the dosing system.
In view of the above, it is an object of the invention to further develop and improve a lubricant dosing apparatus of the above described general type, to achieve a simpler and better operating comfort, and to reliably avoid faulty and erroneous operation thereof. Another, more particular object of the invention is to provide a reliable indication of the proper or improper operation of the dosing apparatus, in a simple manner. The invention further aims to avoid or overcome the disadvantages of the prior int art, and to achieve additional advantages, as apparent from the present specification.
The above objects have been achieved according to the invention in a lubricant dosing apparatus for providing a dosed supply of a lubricant into a pressurized air flow. The apparatus includes a lubricant container, a pneumatically actuated lubricant pump, a lubricant injection channel selectively communicating with an outlet of the lubricant pump, a non-return or one-way check valve interposed between the outlet of the lubricant pump and the injection channel, and an electronic sensor that cooperates or is coupled (e.g. electromagnetically or mechanically) with the non-return valve in such a manner so that the sensor emits an electrical signal responsive to the position or movement of the non-return valve through a defined stroke. When the lubricant pump injects a properly dosed or metered quantity of the lubricant through the pump outlet, the pressurized lubricant temporarily pushes against and opens the non-return valve, causing this valve and particularly its valve stem to move through a resulting stroke with a resulting motion pattern and duration. The motion of the non-return valve stem is indicated by the electrical signal emitted by the sensor, and can be evaluated, e.g. by comparing it to proper signal level thresholds, time points, and/or durations, to determine whether the lubricant dosing operation was carried out properly, i.e. within proper parameters. A faulty operation recognized by this signal evaluation can be used to trigger a fault indication to operating personnel, or to shut down the system.
Thus, the basic feature of the invention is that the non-return valve is coupled with the electronic sensor in such a manner, so that the sensor will emit a corresponding electrical signal when the non-return valve carries out a defined stroke motion. The electrical signal is provided to a control and/or evaluating unit to be evaluated therein, so as to indicate either a successfully and properly completed lubricant dosing and injection cycle, or a fault condition.
In a preferred embodiment, the lubricant pump is embodied as a piston pump, with a dosing needle that is axially slidably guided in a needle bushing, and that withdraws a defined quantity of the lubricant out of the lubricant container via a throughflow port, and then injects this dosed quantity of lubricant into the injection channel, on each working stroke of the pump. The respective dosed and injected quantity of the lubricant is set and fixed (e.g. by the dimensions of the bore of the needle bushing and the stroke travel distance of the dosing needle), for example by the manufacturer of the device. Therefore, the per-stroke injection quantity is not readily externally adjustable (but would require, e.g., replacing the needle and the needle bushing with differently dimensioned components). Thereby, the possibility of an erroneous adjustment of the dosing quantity is avoided. Instead, the desired supply quantity of the lubricant can be electronically controlled, for example by controlling the frequency of dosing injection cycles.
The piston of the lubricant pump is pre-stressed by a compression spring in its neutral or resting position. The spring constant of this compression spring is selected in such a manner, so that the piston can only be moved from the neutral resting position into the working position (or xe2x80x9ccockedxe2x80x9d position), against the force of the spring, once a sufficiently high pre-defined air pressure has been applied to the piston. Then, when the supply of pressurized air is discontinued and the pressure is released, the spring force will return the piston from the working position to the resting position, thereby carrying out a working or injection stroke. Due to this spring-force actuation of the piston during the injection stroke, a constant injection pressure will always be ensured and (unlike air-pressure actuated pumps) will not be dependent on the pressure of the compressed air system, which is subject to fluctuations and varying adjustments. This, together with the abovementioned fixed prescribed lubricant quantity supplied in each injection cycle ensures a relatively consistent stroke of the non-return valve, as long as the viscosity of the lubricant does not vary substantially.
Moreover, since the supplied compressed air must have a sufficient pressure to overcome the constant spring force, for drawing back the lubricant pump piston, a leak or pressure drop in the compressed air system will be readily indicated and recognized in the inventive apparatus, as follows. With an inadequate actuating pressure, the piston of the lubricant pump would not have been drawn back (or xe2x80x9ccockedxe2x80x9d) at all, or would only have been drawn back partially. As a result, the injection stroke would not be carried out at all or only partially, whereby particularly the non-return valve would not move at all or would move improperly, e.g. with a stroke travel that is too short. Any such faulty or non-existent motion of the non-return valve at a time when the valve is expected to carry out its normal stroke travel is detected and indicated by the sensor.
In a further preferred embodiment, the non-return valve has a protruding plug that protrudes from the valve""s valve disk or valve head, so that it reaches into and additionally closes the bore of the dosing needle bushing. Thereby, the length and diameter of this projection or protruding plug determine the minimum stroke travel of the non-return valve for opening the bore of the dosing needle bushing.
According to the invention, the electronic sensor may be any conventionally available sensor that would be suitable for sensing the position or travel of the non-return valve, or particularly its valve stem. Preferably, the sensor is a conventional commercially available inductive or capacitive proximity sensor. The output signal of the sensor can be evaluated in any conventionally known or available evaluation circuit, for example by comparing the output signal to signal level thresholds, or signal durations, or signal waveforms, at each respective time during an injection cycle when a specified signal would be expected based on the expected proper travel or stroke of the non-return valve. By monitoring the stroke travel (or lack thereof) of the non-return valve in this manner, the sensor can directly or indirectly recognize a defect or failure of the pressurized air system supplying air to the dosing apparatus, an empty lubricant supply container, an insufficient or missing quantity of the injected lubricant, and an other fault or complete omission of a respective injection cycle.
Preferably, the injection channel of the apparatus communicates into a main channel, to which compressed air may be supplied through a pneumatic valve. Then, the dosed quantity of lubricant that has been injected through the injection channel into the main channel is blown out of the main channel through at least one outlet, to which an air line or the like may be connected. Thereby, the dosed quantity of lubricant is supplied into the air line, through which it is further conveyed to the machine part or other component which is to be lubricated. In a preferred embodiment of the invention, the operation of the lubricant pump and the supply of compressed air to blow the lubricant out of the main channel can be carried out independently of each other. For example, the pneumatic valve supplying compressed air into the main channel, and the valve supplying compressed air to operate the lubricant pump can be operated and actuated independently. Thus, it is possible to carry out a single lubricant injection cycle to inject a single dose of lubricant into the main channel, followed by several pneumatic blowing cycles. Alternatively, several lubricant injection cycles can be carried out before carrying out a single pneumatic blowing cycle. Thereby, the amount and timing of the lubricant quantity to be provided through the outlet air line or lines can be controlled and adjusted.
A further detail of the invention provides a specialized filling armature or fitting through which the lubricant tank can be filled with lubricant. This helps to avoid damage or failure of the dosing apparatus that would result by filling the container with an incorrect or unsuitable lubricant. In other words, the filling armature or fitting is the only opening through which lubricant may be filled into the lubricant supply container, and this fitting is specially configured so that it only fits a corresponding supply nozzle of the supply of the appropriate lubricant.
The overall construction of the dosing apparatus is selected, designed and executed, using relatively few fabricated parts, with rather small tolerances, so that a high base line accuracy of the dosing volume is achieved. The injected lubricant quantity is fixedly set to a constant amount that will always remain the same. Faulty adjustments of the dosing quantity are no longer possible. All functions of the dosing system are controllable electronically, for example by means of appropriate software, which generates electronic signals to control the pump actuating valve and the pneumatic supply valve of the apparatus. The dosing apparatus includes only a single central pressurized air connection, which supplies the required pressurized air to all functional groups of the dosing apparatus. This also simplifies the handling and connecting of the dosing apparatus.